1. Field of the Invention
The present invention relates to a liquid crystal display device, and further, to technology of an optical film, and more particularly, a phase difference film of a liquid crystal display device.
2. Related Art
In recent years, demand for a liquid crystal display device as a flat panel display has grown since the liquid crystal display device has advantages of thinness, lightweight and being capable of low-power-consumption driving. The liquid crystal display has various modes, and liquid crystal displays using a nematic liquid crystal include a twisted nematic (TN) mode, a vertical alignment (VA) mode, an in plane switching (IPS) mode, an optically compensated bend (OCB) mode and the like. Further, a ferroelectric liquid crystal mode and an antiferroelectric liquid crystal mode in which a response speed is faster than in a nematic liquid crystal are also proposed.
In addition, many other modes are proposed. However, when a liquid crystal display is used as a display, phase difference films 701 are provided outside a liquid crystal 702 and substrates 703 as shown in FIG. 12 not to generate viewing angle dependency of transmitted light intensity and a color. Further, polarizing plates 700 are provided outside the phase difference films 701. This phase difference film 701 is also referred to as an optical compensation film or a phase difference plate.
Although it depends on a liquid crystal mode or a liquid crystal to be used, as for a phase difference film that is used for a liquid crystal display, a uniaxial film and a biaxial film may be stacked.
This phase difference film is usually manufactured by uniaxial or biaxial drawing of a plastic film.
As another method, a phase difference film is also manufactured by using a discotic liquid crystal as described in Patent Document 1.
However, these phase difference films are attached to the outside a substrate so that an adhesion layer is necessary for the phase difference films. In addition, TAC (cellulose triacetate) is necessary to protect the phase difference films. Therefore, in order to manufacture a phase difference film, a structure of several layers stacked is employed, and thus, the thickness is submicron, which results in high cost.
On the other hand, it is also reported that a phase difference film is placed inside a liquid crystal cell in order to reduce cost. (Refer to, for example, a Non-Patent Document 1)
This method provides the following advantages; namely, strong film-adhesiveness, more lightness in weight, and the thinner thickness such as 1 μm to 5 μm.
However, this method is a manufacturing method for only a uniaxial film, and a manufacturing method for a biaxial film has not yet been made clear.
In addition, even when the same uniaxial film is used, it is necessary to change the thickness in order to change a phase difference, since a phase difference is usually determined by Δn×d in the case where the birefringence of a phase difference film is Δn and the thickness is d.
In accordance with this method, a phase difference film is placed between an electrode and a liquid crystal that are provided inside a substrate. Therefore, although the thickness of a phase difference film is thinner, namely 1 μm to 5 μm, the thickness of the liquid crystal is 1.5 μm to 6 μm, and thus, there is caused a problem that voltage is not easily applied to the liquid crystal as compared with a case where the phase difference film is provided outside the substrate.
[Patent Document 1]
Japanese Patent Application Laid-Open No.: Hei8-50206
[Non-Patent Document 1]
B. M. I. van der Zande et al, SID DIGEST, p 194-197 (2003)